In recent years, a thin film of immobilized biologic polymer, functional polymer, organic polymer or the like has been broadly used in an extraordinary variety of applications in high demand such as analytical instruments like a biochip, a biosensor and so on, various display devices, an optical element, a semiconductor element and the like. Although a variety of apparatus and methods for forming such a thin film have been invented and practiced heretofore, the conventional apparatus and methods are not necessarily suitable for forming a thin film by immobilizing a biologic polymer, a functional polymer or the like while maintaining its activity for the following reasons. For example, a spattering apparatus, an EB resistance heating deposition apparatus, a CVD apparatus and the like are put into practical use for forming a thin film of metal or a thin film of inorganic compound. However, since these apparatus are exposed to a plasma or a high heat under a strong vacuum, it is hardly possible to form a thin film by immobilizing a biologic polymer, an organic polymer and the like while maintaining the activity.
An electrostatic coating apparatus is a method of spraying a liquid by pressurized air and adding the electrostatic force thereto so as to provide the attachment to a substrate, and is used for coating and the like. The apparatus, however, requires a huge amount of liquid for the spray by pressurized air and incurs a lot of waste, so is not suitable for forming of a small amount of film of functional polymer or biologic polymer. Moreover, since the diameter of an atomized liquid drop is extremely large in the spray by pressurized air, the liquid drop reaches the substrate without being dried. Thereby, it takes a long time to dry on the substrate, and a biologic polymer, which is easily denaturalized, is liable to lose the activity in the drying process taking such a long time. Therefore, it is difficult to form a film by immobilizing such a substance being easily denaturalized while maintaining the activity with the electrostatic coating apparatus.
A spotting coating apparatus is an apparatus for forming a thin film by applying a liquid onto a substrate with a metal chip or a coater capable of holding a liquid in its micro gap, like the needle gap of a fountain pen, and drying it thereafter. This apparatus also has a lot of problems in forming a film of biologic polymer being more likely to lose the activity, an expensive organic polymer or the like for the same reason, i.e. since the drying time takes long or a lot of materials are wasted.
An inkjet method is a method for forming a thin film by injecting a solvent of the objective functional polymer or the like dissolved therein as a small liquid drop from a nozzle, providing the attachment to a substrate, and drying it. However, it is also difficult to form a thin film by immobilizing a functional polymer or the like while maintaining the activity by this method for the same reason as above, i.e. since the drying time takes long.
An ESD method is a method for forming a thin film by depositing a sample by electrospray (electrostatic atomization) (See Patent Document 1: International Publication No. WO98/58745). This ESD method is more suitable for forming a thin film of biologic polymer or the like than the other methods and apparatus for forming a thin film mentioned above, and is capable of forming a thin film without losing the activity of a biologic polymer or the like under certain conditions. There is, however, a problem in this method that it is difficult to spray a solution with high electric conductivity and the kinds of formable thin films are limited (See Non-patent Document 1: Analytical Chemistry 73, p 2183-2189, 2001). Particularly, a biologic polymer such as a protein is generally dissolved in a buffer solution for keeping pH constant and the electric conductivity is large to be not less than approximately 1000 μS, thereby it is difficult to form a spot or a film by immobilizing it as it is by the ESD method. Also, since a protein and the like lose the activity rapidly in a short time when a stabilizer such as a buffer is removed, the operation for forming a thin film needs to be conducted in a short time and the operating efficiency is down in the case of such a sample. Moreover, there is a problem in that the activity deteriorates even though a thin film can be formed. Furthermore, since the ESD method requires a sample to be almost completely dissolved in a solution for passing through a hole on the tip of a capillary, it is difficult to use a sample being difficult to be dissolved, such as a particle. Additionally, in the ESD method, which is in the form of atomizing microparticles only by the electrostatic force, the atomization rate is very low and the immobilization rate is also very low accordingly.
On the other hand, it is well known that an atomization apparatus using various oscillators has been developed and used in various applications, and an immobilization technique for atomization by oscillation and the electrostatic force in the combination of such a oscillator technique and the ESD method is disclosed (See Patent Document 2: Japanese Patent Application Laid-open Publication No. 2003-136005).